Anilox roll cleanliness is arguably one of the most important considerations in flexographic printing. A dirty anilox roll will reduce its effective volume, resulting in weak printed colors. In turn, this is the root cause for a barrage of issues that includes ghosting, dirty print, color match problems and, ultimately, press downtime.
Dirty anilox rolls correspondingly have a substantial negative impact on repeatability. Improper cleaning techniques, lack of training, improper use of cleaners/cleaning devices and a disregard of attention to detail all attribute to poor anilox roll care, resulting in headaches on press and a loss of potential revenue.
An understanding of anilox cell size is critical to understanding proper cleaning procedures. An anilox’s cells are extremely small. For example, the opening on a 1,200 cpi anilox roll is only 18-μ. the opening on a 600 is 38-μ. To put this into perspective, a human hair is 100-μ. wide. The cells are a fraction of a human hair, and it doesn’t take much to plug them up. To assure these microscopic cells are kept clean, proper cleaning methodologies need to be followed.
A baseline understanding of what it means to actually clean an anilox roll is essential. Just because you wipe down a roll does not mean it is truly “clean.” I am a firm believer in the “prove it” methodology—Prove to me the roll is clean. This can be easily accomplished using a microscope to look at the cells. The key identifier of a clean cell is the white dot in the center. The white dot is the light reflecting back from the bottom of the cell. If you do not see this dot, it means the bottom of the cell is plugged with ink.
Anilox Roll Cleaning Basics
One of the most basic yet important concepts when cleaning the anilox roll is to do so as soon as possible. Letting the rolls sit in the press, not rotating or without a supply of ink, will cause that ink to dry in the cells. To prevent this, keep the ink and rolls circulating. This will keep the ink wet and make it much easier to clean up. Remember how small the cells are: It does not take long for the ink to dry. The level of cleaning difficulty increases exponentially as the ink dries or cures in the cells.
Handle your anilox rolls with care. The anilox rolls are typically safest in the press and the most damage occurs when they are moved. Keeping the rolls covered will decrease this risk. Use two hands to carry the anilox rolls to assure you have a solid grip. Do not lift the rolls by the gears or bearings. I have seen operators do this with the set screw loose and the anilox roll bounced on the floor. I am sure their supervisor wasn’t too happy about this. Also, do not carry anilox rolls over your shoulder. They are not properly supported and an increase in damage is likely.
Ceramic is hard, but any major impact can damage a roll. If it isn’t outright chipped or damaged, it more than likely will develop small cracks. These cracks allow cleaners to migrate under the ceramic and will grow over time, creating even more issues. Keep metal objects like Allen wrenches, screwdrivers and ink knives away. If an anilox is set on a table, make sure it is clean and free of debris; I recommend setting the anilox roll on a bed of towels or a stand that keeps the engraving surface from touching anything. And don’t drag a roll across countertops or other surfaces, as it is likely to be scratched.
Don’t forget to clean the ends of the rolls. The ends of the rolls are commonly overlooked when cleaning, especially with UV ink. One spot of UV ink can spread to the face of the roll in a hurry. Many times, ink will build up on the ends of the roll, especially after long runs. Operators will commonly use a metal paint scraper or screwdrivers to remove this dried ink. This is not a recommended practice. Use a plastic scraper instead of metal. The likelihood of damaging the roll is far less with plastic than it is with metal.
Unquestionably, the most overlooked step when cleaning anilox rolls is rinsing and drying. Rinsing the rolls will remove any cleaner that may be left and eliminates the possibility of it causing corrosive damage. It also assures the ink debris is flushed away, leaving a roll that is actually clean. Failure to dry the roll will cause water spots. Sadly, this is a common occurrence in many pressrooms and can show up in print. Water spots can be easily avoided by rinsing and drying rolls after cleaning. A 50/50 mix of isopropyl alcohol and water will aid in rinsing and drying. Make sure to completely dry a roll before applying its cover. Failure to do to so will trap any solvents or liquids on the surface. They can then migrate to the base metal and cause issues as well as a camouflaging pattern.